Thermal time delay relay



1963 A. L. BASTIAN THERMAL TIME DELAY RELAY Filed June is, 1960 JNVENTOR. ARTHUR L. E|A5TIAN HIS ATTDRNEY United States Patent Oihce 1 3,976,381 THERMAL TlME DELAY RELAY Arthur L. Bastian, Hackensaclr, Ni, assignor to Curtlssll right Corporation, a corporation of Delaware Filed June 13, N60, Ser. No. 35,516 8 Claims. (@l. 266-122) This invention relates to thermal time-delay relays and has for its principal object an improved relay of this type that is capable of sensitive and cfficient operation under vibration conditions, is adapted for low-cost manufacture, and has adequate flexibility for practical use.

Heretofore, some forms of thermal time-delay relays have used a longitudinal metal strip subject to elongation upon application of heat, for operating through other means a switch or circuit controlling contacts according to expansion or contraction of the strip. Such relays have in some cases been found unsatisfactory under conditions of severe vibration, and in other cases stability is obtained only by the utilization of additional members in relatively involved designs. For example, without the introduction of tension a conventional thin, heat responsive member designed for a short operating time tends to resonate at comparatively low natural frequencies, whereas a heat responsive member of greater mass would require for flexibility a reduced section or hinged member, w ich combined with the greater mass would tend to resonate at relatively low frequencies and therefore be undesirable for many applications.

In accordance with this invention the above problem is basically solved by using a thin, low mass, high tensile strength element that is placed under initial tension and is coupled to a more rigid and massive temperature compensation member that is in turn placed under compression and moment-loaded by the tension element. This element constituting the actuator acts in concert with the cantilever spring action of the compensator which opposes the tension movement of the actuator. Variation in length or" the actuator is produced by energized and deenergizing the heater associated therewith which produces in the disclosed form change in length of the actuator by virtue of the temperature coeiiicient of expansion of the actuator material.

By means of this arrangement, low natural frequencies are avoided, the required thermal time-constant is obtained and t. e tension-compression action further provides sensitive and accurate operation of the relay contacts. The arrangement also lends itself to dir erent types or" contact operation; for example, the above-described or motive unit of the relay may directly or indirectly control simple make-and-break contacts for single or double pole switch ing, as Well as snap-action contacts.

The principle of this invention can of course be applied to obtain a large thermal time-constant where required, by increasing the mass of a heat responsive structure that is connected to the tension strip.

The invention will be more fully set forth in the following description referring to the accompanying drawing, and the features of novelty will be pointed out with particularity in the claims annexed to and forming a part of this specification.

Referring to the drawing,

FIG. 1 is an elevational side view, partly in section, showing the relay in the deenergized or unheated position;

FIG. 2 is an enlarged sectional view taken along the line 2-2 of FIG. 1;

FIG. 3 is an elevational front View of the relay of FIG. 1;

FIG. 4 illustrates in more detail the configuration of the temperature compensator;

FIG. 5 illustrates the relay in a metallic envelope with Patented Feb. 5, 1953 2'. provision for external adjustment; and FIG. 6 is an exploded view showing in part in greater detail the compensation, actuator or tension strip, and heater unit.

Referring to PEG. 1, the relay comprises essentiall relatively moveable contacts 1 and 2 for controlling exterior circuitry (not shown). The contact 1 is normally fixed and may be adapted for adjustment as indicated at It for calibration purposes. The movable contact 2 is carried at one end of a member 3 that also constitutes an ambient temperature compensator as described later. The member 3 is an elongated metal bar or strip of special configuration for temperature compensation and is fixed to base structure generally indicated at 4 at its lower end. At its upper end it carries, or is suitably connected to the movable contact 2. It is also connected at both its upper and lower ends, at 5a and 5b, as by spot weld ing, to a thin, elongated, low mass, metal strip 5, the lower ends being united while the strip is held under tension. This strip constitutes the heat responsive element. It may suitably be composed of type 392 or 304 stainless steel which is rugged and has high tensile strength and a high thermal coefhcient of expansion. The strip is preferably in elongated rectangular form so as to provide comparatively large heat-transfer area with the attached heater unit 6, which also is of low mass.

The heater unit which may be of conventional form, FIGS. 1, 3 and 6, comprises a heating wire 7 wound around a rectangular strip of mica a; that is in turn riveted to the element 5 at S as shown. The wire 7 is suitably insulated from the metal strip 5 by a thin mica sheet 8a, FIG. 6. The terminals 7a, 7b of the heating coil are connected through control circuitry to a suitable voltage supply (not shown), the external connections of the relay forming no part of the present invention so that illustration thereof is unnecessary.

The operation of the device is as follows: the heat rcsponsive strip 5 or actuator is contracted and under maximum tension during the deenergized or cool state the heater. In this condition, the compensator or compression member 3 is bowed slightly toward the strip 5 so that the contact 2 is drawn away from contact 1. Accordingly the relay control circuit is open at contacts 1-2.

When the heater is energized, the temperature of the strip 5' increases and the strip expands, i.e. elongates, thus decreasing the compression on member 3 so that the latter in turn tends to straighten and move the contact 2 toward engagement with contact 1. The time required for this operation, i.e. the operating time of the relay, is determined by the rate of heat transfer from the eater to the tension strip, the mass of the strip and its configuration; it is also afiected by the configuration and character of the compression or compensator member 3 and the character or" the surrounding gas or ambient medium. There is no immediate effect of the heater on the relatively massive structure of the com pensator. Accordingly there is no appreciable lost motion due to unwanted compensator expansion tending in effect to cancel the expansion of the actuator.

As above stated, a typical design has a comparatively small thermal time-constant, such as of the order of about ten seconds. The accepted definition of the thermal time-constant is the time required for the contact to move through 63.2% of its travel. The contacts which may be of silver or other suitable contact material, remain in engagement as long as the heater is energized, and disengage when the heater is shut oil and the strip 5 subsequently contracts. For snap-action operation, the up per end of the member 3 instead of directly carrying the movable contact, may engage the actuating element of a snap-action switch of suitable type, such as a microswitch for operation generally as above described.

The compensator or compression member 3, FIGS. 1, 2, 4 and 6, is shown as a metallic bar or strip disposed generally parallel to and opposite'the heat responsive strip 5. It is materially more rigid and rugged and has greater mass than the strip 5 and is composed of the same material or one having a similar expansion rate. A main intermediate portion is dished as indicated along the main part of the longitudinal axis, FIGS. 2, 4 and 6, so as to be concave with respect to the strip 5. The terminal portions are'ofi-set inwardly toward the strip 5 at 3a and 3b so that the main dished portion is spaced from the heat responsive strip. This provides both the required rigidity, and suitable spacing between the parts for minimizing heat-transfer thercbetween. The configuration thus lends itself to ambient temperature compensation, i.e., upon increase in ambient temperature for example, the tension strip and the compensator 3 both tend to expand; however the compensator is restrained by the pre-tensioned strip 5 so that the ambient temperature effect on the latter counteracts the tendency of the compensator to warp in a direction to cause closing movement of the contact 2. No movement of the contact 2 therefore takes place during change in ambient temperature within the rated range. The converse is true where the ambient temperature decreases.

This the elfect of change in concurrently affects both the is compensated so that the operating time of the relay is substantially uniform for all usual ranges of ambient temperature.

In FIG. 5 there is shown a practical application of the relay to sealed-in operation. The relay is suitably mounted within a sealed metal envelope having a flexible end-wall or diaphragm 11 through which is sealed an adjusting member 12 for the relatively fixed contact 1. The member 12 is offset at 12a so as to carry an adjusting screw 13 and the inner end 121) carries an insulating member such as a glass ball 14. This ball engages the contact 1 which in turn is carried on a flexible support 15. Thus calibration of the contacts may be obtained simply by adjusting the set screw 13.

Summarizing: by reason of the pretensioned heat responsive strip and its integral connections at opposite ends with the corresponding ends of the comparatively rigid and massive compensator 3, and the thin low mass combined construction of heater, the thermal time delay of the present relay is such that in the form shown a short thermal time-constant is provided together with sensitive and efficient operation; The rugged construction coupled with the high frequency of natural resonance also enables the relay to withstand severe vibration tests, especially as low natural frequencies are avoided.

It should be'understood that this invention is not limited to specific details of construction and arrangement thereof herein ambient temperature, which modifications may occur to onev skilled in the art without departing from the spirit of the'invention.

What is claimed is: s

1. A thermal time delay relay having coacting switch contacts and means for activating said contacts for thermal time-constant operation comprising a low-mass metal strip having high tensile strength and a high thermal coefficient of expansion, a comparatively rigid, elongated ambient temperature compensating member having large mass as compared with said strip and having a configuration for resisting bending moment, said contacts being operatively connected'to one end of said compensating member, said strip being connected between the opposite ends of said member under initial tension so that said member is normally under compression due to bending moment, and a heater in heat-transfer illustrated, and that changes and.

relation thereto for causing decrease and increase of tension on said strip according to the condition of the heater, said change in tension varying the bending moment on said compensating member for causing control movement of said contacts.

2. A thermal time delay relay wherein the compensating member has an elongated barlike form with an intermediate portion that is dished along its longitudinal axis and concave with respect to said high tensile strip so as to increase the rigidity of said member, the opposite ends of said member being off-set so as to increase the space between the dished portion of the compensating member and said strip thereby to minimize head transfer therebetween.

3. A thermal time delay as specified'in claim 1 wherein decrease and increase of tension on said strip is caused by energization and deenergization respectively of the heater.

tension strip and heater unit,

the heat responsive strip and j 4. A thermal time delay relay as specified in claim 1 wherein one of said coasting contacts is carried at a common connection of said compensating member and tension strip. 7

5. A thermal time delay relay having relatively mov able switch contacts and means for effecting engagement and disengagement of said contacts for short time-constant operation, said means comprising an elongated, low mass, heat-responsive member adapted for longitudinal expansion when heated, a heater disposed adjacent said member, a comparatively rigid ambient temperature compensating member disposed generally parallel to said heat responsive member and spaced therefrom to minimize heat transfer therebetween, each of said members having one end thereof fixed as to relative movement and the other end connected to the corresponding end .of the other member, said heat responsive member being connected to the compensating member under initial tension so that the compensating member is in turn under compression and bending moment in the now operated condition of the relay, whereby said connected ends move together in a generally lateral direction in response to expansion and contraction respectively of the pretensioned heat responsive member, the switch being arranged so as to be controlled by said lateral movement.

6. A thermal time delay relay as specified in claim 5 wherein the heat responsive and compensating members are integrally joined under initial tension at their fixed and movable ends.

7. A thermal time delay relay as specified in claim 5 wherein the heat responsive member comprises an elongated low mass strip of high tensile steel having a high thermal coefficient of expansion and the more massive and rigid compensating member under compression has a similar coefficient of expansion and is bowed toward the heat responsive member due to the pretensioned condition of the latter.

8. A thermal time delay relay as specified in claim 5 wherein the low-mass heat responsive member is a strip that is comparatively thin and flat and has closely mounted thereon a low-mass heater unit that is likewise thin and flat, the combined low-mass 0f the pretensioned member and heater unit precluding low natural frequencies.

References Cited in the file of this patent UNITED STATES PATENTS FOREIGN PATENTS 20,085 Great Britain ....1 Sept. 5, 1913 as specified in claim 1 

1. A THERMAL TIME DELAY RELAY HAVING COACTING SWITCH CONTACTS AND MEANS FOR ACTIVATING SAID CONTACTS FOR THERMAL TIME-CONSTANT OPERATION COMPRISING A LOW-MASS METAL STRIP HAVING HIGH TENSILE STRENGTH AND A HIGH THERMAL COEFFICIENT OF EXPANSION, A COMPARATIVELY RIGID, ELONGATED AMBIENT TEMPERATURE COMPENSATING MEMBER HAVING LARGE MASS AS COMPARED WITH SAID STRIP AND HAVING A CONFIGURATION FOR RESISTING BENDING MOMENT, SAID CONTACTS BEING OPERATIVELY CONNECTED TO ONE END OF SAID COMPENSATING MEMBER, SAID STRIP BEING CONNECTED BETWEEN THE OPPOSITE ENDS OF SAID MEMBER UNDER INITIAL TENSION SO THAT SAID MEMBER IS NORMALLY UNDER COMPRESSION DUE TO BENDING MOMENT, AND A HEATER IN HEAT-TRANSFER RELATION THERETO FOR CAUSING DECREASE AND INCREASE OF TENSION ON SAID STRIP ACCORDING TO THE CONDITION OF THE HEATER, SAID CHANGE IN TENSION VARYING THE BENDING MOMENT ON SAID COMPENSATING MEMBER FOR CAUSING CONTROL MOVEMENT OF SAID CONTACTS. 